A transfer feeder for transferring a work between the working stations in succession is conventionally placed in a transfer press including a plurality of working stations in a press main body. The transfer feeder includes a pair of parallel transfer bars at left and right with respect to a work transfer direction, and each of the transfer bars has a long length to extend along all the working stations.
As a conventional transfer feeder, the one is disclosed in, for example, in Japanese Patent Laid-open No. 11-104759, and according to the Laid-open Patent, a pair of left and right transfer bars are constituted by long integrated bars extending along all the working stations. The transfer bar is provided with a plurality of suction tools with predetermined spaces from each other in the work transfer direction to be ascendable and descendable, and movable in the lateral direction (clamp direction) and the longitudinal direction (transfer direction) by a linear motor. As a result, it is made possible to correspond to a change of the work in the clamp/unclamp direction by the aforementioned suction tools when transferring a work.
As another example of the prior art of the transfer feeder, for example, the one disclosed in Japanese Patent Laid-open No. 10-314871 is cited. According to the Laid-open Patent, in the transfer feed bar drive device, the transfer bar (feed bar of the same Laid-open Patent) includes a feed carrier, to which the transfer bar is connected so as to be movable up and down and in the lateral direction and restricted in the movement in the longitudinal direction, and a feed unit for moving the feed carrier back and forth by a linear motor.
As still another example of the prior art of the transfer feeder, the one is disclosed in for example, Japanese Patent Publication No. 7-73756. According to the same Patent Publication, a plurality of carriers are provided at a pair of vertically movable guide rails at left and right with respect to the work transfer direction (corresponding to the aforementioned transfer bar) to be independently movable by a linear motor. The cross bar is spanned between the carriers opposing each other with each working station between them, a work is sucked with the work holding means including the cross bar, and the cross bar is moved along the guide rail by the aforementioned linear motor, whereby the work is transferred.
However, the above-described conventional transfer bar has the following problems.
The transfer bars described in Japanese Patent Laid-open No. 11-104759 and Japanese Patent Laid-open No. 10-314871 are each constituted by an integrated bar extending along all the working stations, and there is only one system of the driving source in the feed direction. Consequently, adjustment of each stroke of the feed, lift, and work transfer height (so-called feed level) of each process has limitation to some extent. Namely, concerning the feed stroke, the transfer pitch (distance between the processes) is constant, and therefore the work transfer is difficult in the transfer press in which the pitches between the adjacent working stations differ. In addition, the die has to be designed so that the distances between the processes are equal, which causes the problem that it is difficult to design an optimal die in consideration of the interference curve and the like. Further, concerning the lift and work transfer height, they have to be equal between the respective working stations, which makes it difficult to design an optimal die corresponding thereto.
The transfer bar described in Japanese Patent Publication No. 7-73756 is constituted so that a plurality of carriers can be self-propelled independently by the respective linear motors. However, there arises the problem that the lift stroke and the work transfer height cannot be adjusted for each process since the transfer bars (guide rails) are constituted by integrated bars extending along a plurality of working stations as described above.